To measure various characteristics of a measurement target object, methods of irradiating the measurement target object with light and detecting reflected light by an imaging device are commonly used.
For example, Patent Literature 1 discloses a coloration substance quantitative determination device that performs a quantitative determination of a coloration substance contained during the solid phase by detecting reflected light from the solid phase. Patent Literature 2 discloses a color reader that reads a color image of an original by irradiating the original with light and detecting reflected light. Patent Literature 3 discloses a system that captures multi-spectral or hyper-spectral images and is capable of scanning a two-dimensional image (multi-spectral image or hyper-spectral image) having more than three bandwidths.
On the other hand, an image sensor generally outputs an electrical signal (pixel signal) depending on the amount of incident light. To obtain a desired output that is sufficient to perform a measurement or image capturing, the corresponding amount of light is necessary to be incident on the image sensor. If an efficient incidence of light from a light source on an image sensor is possible, even when the amount of irradiation from the light source is relatively small, the measurement or image capturing can be implemented with higher sensitivity.
For example, Patent Literature 4 discloses an inspection light irradiation device that includes a cylindrical light condenser having a mirror-finished inner surface provided in an optical path along which the irradiation light from a light source is guided to an image sensor, and an inspection device of solid-state image sensor using it.